Why won't the Internet work this way on my Linksys RV042?!

Hey guys,
I have a Linksys RV042 router, which supports two WAN Internet connections. WAN1 is connected to an ADSL2 modem, in bridged mode and works fine.
WAN2 is plugged into a Three Mobile Broadband ethernet box, but I cannot get it working.
The Three ethernet box establishes the connection itself, and works fine when plugged into a laptop. However, when plugged into the WAN2 port on the RV042, I can't browse the net. UNLESS I change the RV042 to work in 'gateway' mode rather than 'router' mode which it is currently in.
WAN2 is configured with a static IP of 192.168.2.2, and the Three ethernet router is 192.168.2.1. The default gateway, and DNS also point to the Three box at 192.168.2.1.
Does anyone have any suggestions as to why it doesn't work in router mode, only gateway mode? I need the RV042 in router mode for the way an email server is setup.
$30 cash reward to the person who helps me solve this problem once and for all!
Cheers

The only ways I can see it working would be to:
A) make the 3 wireless modem a bridged modem (may/may not be possible, does it have any options for it?) and then do the normal thing.
or
B) Do what you are currently doing and set the 3g modem to portforward to the RV042 and the portforward the RV042 to the inside service.
The problem appears to be the 3g router not wanting to act as a straight bridged modem.
Edit --> Did a bit of extra reading, the device is a rebadged Huawei D100 Router.
Have you tried web browsing to it? The username and password are admin.
I'd also try seeing if you can telnet to the box also and see if it gives you any options.

It doesn't have a bridged mode, the D100 creates the connection itself. I have tried port forwarding 0.0.0.0 subnet 0.0.0.0 (everything) to 192.168.2.1 (the D100) but it still didn't work? The D100 doesn't seem to have any options for port forwarding. However, as I said before, it works fine when the RV042 is in 'gateway' mode as opposed to 'router' mode?!

The only ways I can see it working would be to:

A) make the 3 wireless modem a bridged modem (may/may not be possible, does it have any options for it?) and then do the normal thing.

or

B) Do what you are currently doing and set the 3g modem to portforward to the RV042 and the portforward the RV042 to the inside service.

The problem appears to be the 3g router not wanting to act as a straight bridged modem.

Edit --> Did a bit of extra reading, the device is a rebadged Huawei D100 Router.

Have you tried web browsing to it? The username and password are admin.
I'd also try seeing if you can telnet to the box also and see if it gives you any options.

One issue you may experience is double NAT although if your local subnet is something other than 2.x then it should still work.

If your Linksys RV042 router has a LAN address of say, 192.168.1.1 and your local computers have their gateway and DNS set to 1.1 and the router understands that 2.2 is it's default gateway and DNS it will work but, as suggested, you are going to be doing this via double NAT.

Disclaimer: this post may have been made via a mobile device. All formatting, grammar and the possible hilarious substitution of key words should be attributed to the autocorrect features of the mobile device and likely has nothing to do with the idiot driving it.

They are on different subnets, the RV042 router has a 203.x.x.x address as it hosts a mail server. When running on the Three Ethernet modem, and I tracert an external IP, it gets as far as the LAN address of the RV042 router (not even getting to the 192.168.2.2 address of the WAN2 port!).

I have set up a port forward for IP 0.0.0.0 subnet 0.0.0.0 to go to 192.168.2.1 (the 3 modem) with 10 hops. But it just doesn't work?

What is your local subnet? Is it also 192.168.2.x?

One issue you may experience is double NAT although if your local subnet is something other than 2.x then it should still work.

If your Linksys RV042 router has a LAN address of say, 192.168.1.1 and your local computers have their gateway and DNS set to 1.1 and the router understands that 2.2 is it's default gateway and DNS it will work but, as suggested, you are going to be doing this via double NAT.

The router seems to be getting confused, as one IP is getting assigned to two devices.

Try setting the ethernet box to use IP 192.168.2.2 becuase the ADSL modem might already be using 192.168.2.1.

I don't think that is it, the ADSL modem is on a different subnet again (192.168.20.1). When I unplug the ADSL modem, it fails over to the WAN2 port and attempts to use the Three GSM ethernet box modem.

The router seems to be getting confused, as one IP is getting assigned to two devices.

Try setting the ethernet box to use IP 192.168.2.2 becuase the ADSL modem might already be using 192.168.2.1.

I don't think that is it, the ADSL modem is on a different subnet again (192.168.20.1). When I unplug the ADSL modem, it fails over to the WAN2 port and attempts to use the Three GSM ethernet box modem.

I don't think anything should be using 192.168.2.1 apart from the router itself, so try re-assigning the modem to 2.2 and the ethernet box to 2.3, both as static.

Ok so,
Your local subnet is 203.x.x.x
The subnet of your ADSL is 192.168.20.x
The subnet of your 3G connection is 192.168.2.x
I am assuming all with a class C subnet mask of 255.255.255.0
The RV042 works fine in router mode with ADSL - not with 3G.
I am assuming your ADSL modem is performing all your internet connection hoo hah, the same as the 3G modem is.
You don't need to set a 0.0.0.0 port forward, in fact I would remove it. If the RV042 is designed to work with redundant links it shouldn't need it for basic internet access.
Can you confirm that what I have summarised is correct?

Disclaimer: this post may have been made via a mobile device. All formatting, grammar and the possible hilarious substitution of key words should be attributed to the autocorrect features of the mobile device and likely has nothing to do with the idiot driving it.

Your local subnet is 203.x.x.x
The subnet of your ADSL is 192.168.20.x
The subnet of your 3G connection is 192.168.2.x

I am assuming all with a class C subnet mask of 255.255.255.0

The RV042 works fine in router mode with ADSL - not with 3G.

I am assuming your ADSL modem is performing all your internet connection hoo hah, the same as the 3G modem is.

You don't need to set a 0.0.0.0 port forward, in fact I would remove it. If the RV042 is designed to work with redundant links it shouldn't need it for basic internet access.

Can you confirm that what I have summarised is correct?

Yes, everything you summarised is correct. I only added the port forward in becuase it wasn't working, I have removed it again now. The only other piece of information I have is that the Three ethernet modem gains a dynamic WAN IP of 10.x.x.x when it goes on the net. This isn't static, and is assigned by the Three network servers I assume.

Isn't 203.xxx a public address space?
I am not sure how much work it is (regarding your local LAN) but to keep it simple I would probably have gone with
Local subnet: 192.168.1.x, netmask 255.255.255.0
ADSL: 192.168.2.x, netmask 255.255.255.0
3G: 192.168.3.x netmask 255.255.255.0
ADSL WAN Port: 192.168.2.1
ADSL router: 192.168.2.2
3G WAN port: 192.168.3.1
3G Modem: 192.168.3.2
The thing is, I think you are doing this the wrong way.
The router can initiate PPPoE connections and should be able to authenticate for you. Putting your modems into bridged mode will allow you to dictate logins via the linksys router. This will ensure that the public IP addresses reside at the router allowing for simpler routing and removes the double NAT problem.

Disclaimer: this post may have been made via a mobile device. All formatting, grammar and the possible hilarious substitution of key words should be attributed to the autocorrect features of the mobile device and likely has nothing to do with the idiot driving it.

In addition to The Tick's points of clarification above, has the 203.x.x.x space been assigned to you by your ADSL ISP?
If so, do you need to receive inbound e-mail on your server or are you only sending outbound mail from it?
Lastly - in Linksys speak, what's the difference between gateway & router mode?

Yes, the 203.x.x.x is provided as a static IP from our ISP. We are runnign our own mail server, so we are sending and receiving emails.
Unfortunately, the 3 GSM modem can't be run in bridged mode, with PPP, so I have no option other than assigning a static IP to it. This is the problem I am trying to get around. :(

Right. Well for a start, you're unlikely to be able to send packets out of the 3G connection with a source IP address in that range and you certainly won't be able to receive packets back in on that interface destined for your allocated block - all traffic to and from your 203.x.x.x subnet MUST go via your ADSL connection.
Is your goal here to have your mail server sending/receiving as is, plus have the benefit that if the ADSL connection goes down, the 3G service can be used as a backup? Or are you trying to load balance across the connections? The latter would likely cause more problems than it's worth.
Linksys' web site sucks too many balls for me to be able to find the manual (it couldn't possibly be my fault, right?) but here are some general ideas.
I can see two main options. Neither of them are easy. There are other variants but I don't know what the capabilities of the RV042 are. Both of the below are variants of The Tick's description above.
1. Public addresses on inside:
* configure the RV042 to do PPPoE over the ADSL connection (as you already have) and do plain IP routing to the 3G device.
* Set the ADSL connection to be the primary link and the 3G to be the backup
* Do *not* perform NAT on the RV042 for traffic outbound on primary link
* Avoid performing NAT on the RV042 for traffic outbound on the secondary (3G) link as the 3G router will do this anyway. If you don't do NAT for this traffic on the RV042 you'll need to set a static route on the 3G router/modem so it knows how to reach your LAN (public addresses) via the RV042's WAN2 interface.
2. Private addresses on inside:
* Configure private IP address space on the 'LAN' side of the RV042 INCLUDING ON THE MAIL SERVER
* configure the RV042 to do PPPoE over the ADSL connection (as you already have) and do plain IP routing to the 3G device.
* Set the ADSL connection to be the primary link and the 3G to be the backup
* Perform NAT on the RV042 for traffic outbound on primary link
* Avoid performing NAT on the RV042 for traffic outbound on the secondary (3G) link as the 3G router will do this anyway. If you don't do NAT for this traffic on the RV042 you'll need to set a static route on the 3G router/modem so it knows how to reach your LAN (private addresses) via the RV042's WAN2 interface.
* Set a static NAT rule on the RV042:
-- Inbound interface: WAN1
-- Traffic source: ANY; destination: Mail server public IP addr; TCP port 25
-- Action: rewrite/redirect to Mail server private (actual assigned) IP address on LAN; TCP port 25
Note that in both scenarios, outbound mail MAY work in some cases if the ADSL link goes down, but inbound mail will NOT work. Web browsing and similar should be fine in both cases.
If there are any other devices (routers, firewalls, PCs etc.) on the inside of this network that you haven't mentioned so far, you should consider the impact of the above changes on those devices and/or describe them here.
The above advice comes with no guarantee and is to be implemented at your own risk based on your own analysis of the potential impacts.